I would maybe attack the problem from a different view.

Your thinking is to prevent the "fuel splash" from getting into the interior after the crash, which is a very GOOD idea.

But, how about doing more to keep the fuel contained "inside the fuel tank" during the crash? Fuel foam will reduce the fuel from sloshing out of the damaged tank after the crash. It does not have much reduction to the volume of the tank. Look into what is available from the fuel cell suppliers. They sell it in blocks that you squeeze and slide it into the tank through the filler. We have it in our VW drag car which has a small aluminum tank mounted "up front" which IMO is an even worse location than being hit from behind.